Anthropic confirms an investigation: Claude Mythos Preview appears to have been accessed without authorization

According to a Bloomberg News report dated Tuesday, April 22, 2026, citing documents and people familiar with the matter, Anthropic’s Claude Mythos Preview AI model was accessed by a small batch of unauthorized users on the same day Anthropic first publicly announced its plan to open up Mythos testing to a limited number of enterprises.

Bloomberg Report Details: A Small Number of Users Received Access to Claude Mythos Preview

According to the Bloomberg report, a small number of users in a private online forum obtained access to Claude Mythos Preview on the same day that Anthropic announced its plan to open up Mythos testing to a limited number of enterprises. Since then, that user group has continued to use Mythos regularly, but Bloomberg noted that the purpose was not for cybersecurity use. Bloomberg said that, in reporting on this investigation, the access party provided screenshots and an on-site demonstration of the model’s use.

An Anthropic spokesperson confirmed that an investigation has been launched and did not provide further details on the progress of the investigation.

Background on Claude Mythos and Project Glasswing

According to Anthropic’s public information, Claude Mythos Preview was announced on April 7, 2026, as part of Anthropic’s “Project Glasswing.” Project Glasswing is a controlled program that allows specific organizations to use an unreleased Claude Mythos Preview to perform defensive cybersecurity work. Anthropic previously said that Mythos has unprecedented capabilities to identify digital security vulnerabilities and potential misuse, and that it has drawn the attention of regulators.

Frequently Asked Questions

When did Bloomberg report the unauthorized access to Claude Mythos Preview?

According to a Bloomberg News report dated Tuesday, April 22, 2026, citing documents and people familiar with the matter, Claude Mythos Preview was accessed without authorization by a small number of users in a private forum on the same day Anthropic announced plans to open up testing to limited enterprises.

What official response did Anthropic give to this incident?

According to an Anthropic spokesperson statement cited by Bloomberg, Anthropic said: “We are investigating a report that claims someone accessed Claude Mythos Preview without authorization through one of our third-party provider environments.”

Which program does Claude Mythos Preview belong to, and what is its intended use?

According to Anthropic’s public information, Claude Mythos Preview was announced on April 7, 2026, and is part of the “Project Glasswing” program, allowing certain organizations to use the unreleased model for defensive cybersecurity work.